1. Field of the Invention
The present invention relates to a sheet conveying device for conveying a sheet to an image forming section, and an image forming apparatus provided with the same, such as a digital copying machine, laser printer and the like. Particularly, it relates to a sheet jam processing function at the time of sheet conveyance.
2. Description of the Related Art
A conventional image forming apparatus is provided with an image forming section at a center thereof. In the image forming section, a predetermined image is formed by respective steps of charging, exposing, developing, and transferring. In order to form a fine image by using the image forming section, it is necessary to control the timing at which a sheet is conveyed to the image forming section and to correct an oblique conveyance of the sheet. For this reason, the conventional image forming apparatus is provided with a sheet conveying device including a registration roller and peripheral members thereof as disclosed in Japanese Unexamined Patent Publication No. Hei. 5-58500.
FIG. 9 is a cross sectional view showing a periphery of the sheet conveying device provided in the conventional image forming apparatus. In FIG. 9, a photoconductive drum (not shown) is accommodated inside a drum unit 20. A transferring roller 16 is provided beneath the drum unit 20. The photoconductive drum and the transferring roller 16 are used to transfer a toner image onto a sheet conveyed by a pair of registration rollers 14. A pair of conveying rollers 13 for conveying the sheet conveyed from a sheet supplying cassette or a stuck bypass (not shown) to the pair of registration rollers 14 are provided on an upstream of the pair of registration rollers 14 in the sheet conveyance direction.
In a state that the registration rollers 14 are suspended, a leading end of the sheet conveyed through the pair of conveying rollers 13 and the sheet conveyance passage 22 comes into contact with a nip portion of the pair of registration rollers 14 and the oblique conveyance of the sheet is corrected. Thereafter, the pair of registration rollers 14 are driven to convey the sheet in synchronization with the timing of the image formation of the image forming section. A registration guide 23 is provided above the sheet conveyance passage 22 between the pair of registration rollers 14 and the pair of conveying rollers 13.
A detecting sensor 24 detects a presence of the sheet which passes through the sheet conveyance passage 22, and is provided in the vicinity of the registration guide 23 in such a manner that an emitting surface of the detecting sensor faces the sheet conveyance passage 22. The detecting sensor 24 detects a passing of the leading end of the sheet, and the detection is sent to a controlling section (not shown) of a main body of the image forming apparatus. A contact-making amount (slackness amount) of a sheet against the pair of registration rollers 14 is determined by controlling the time period from the passing of the leading end of the sheet to a stopping of the driving of the pair of conveying rollers 13 by the controlling section. Further, the detecting sensor 24 detects a non-standardized sheet by continuously detecting the sheet from the leading end to the tailing end to detect a size of the sheet. The sheet size is used when the controlling section determines a suspension time of the pair of registration rollers 14 and a suspension time of the image formation.
FIG. 10 is a perspective view showing an image forming apparatus in which a developing unit 5 positioned above the sheet conveyance passage 22 is taken off, and a sheet jam processing is conducted from above. FIG. 10 shows the state that the developing unit 5 is taken off, and a part of the main body including the drum unit 20, the registration guide 23, and the like is omitted. An upper portion of the sheet conveyance passage 22 is opened from a stuck bypass 11b to the pair of registration rollers 14 (see FIG. 9.) by taking the developing unit 5 off to conduct the sheet jam processing in the sheet conveyance passage 22.
In the foregoing conventional image forming apparatus, the registration guide 23 (see FIG. 9.) is so designed to be pivotable in upwardly and downwardly about a pivot positioned in the vicinity of the registration rollers 14. Thus, when the sheet jam processing is conducted, the registration guide 23 is rotated toward the side of the drum unit 20 to remove the sheet.
However, a user is required to stretch his/her arm into a narrow space in the vicinity of the pair of the registration rollers 14 to rotate the registration guide 23 to remove the jammed sheet. In addition to that, the space for the pivotal of the registration guide 23 is limited due to the drum unit 20 positioned above the pair of registration rollers 14. Accordingly, it has not been easy to conduct the sheet jam processing. Further, there is not any means for rotating the registration guide 23. Consequently, the operation is troublesome.